1. Field of the Invention
The present invention relates to a portable IC card, referred to here as a carrier, of the non-contact type and, more particularly, to a non-contact portable carrier which is supplied with power through an electromagnetic coupling.
2. Description of the Related Art
FIG. 6 shows the construction of a known non-contact portable carrier of electromagnetic coupling type. The non-contact portable carrier 9 has a power receiving coil 10 to which is connected a full-wave rectifier circuit 11. A smoothing capacitor 12 and an integrated circuit 13 (referred to as "IC" hereinafter) for controlling and processing signals are connected to the full-wave rectifier circuit 11. The smoothing capacitor 12 has a high-voltage terminal and a grounding terminal. A signal transmitting/receiving coil 14 is connected to the IC 13 through a received signal detecting element 15 and a signal transmitting element 16.
The portable carrier 9 thus constructed is set on a terminal device 1. The terminal device 1 has a power supplying coil 2 and a signal transmitting/receiving coil 6 which are disposed adjacent the coils 10 and 14 of the portable carrier 9 set on the device 1. A power source 3 and a voltage regulator 5 are connected to the power supplying coil 2. A voltage detector 4 for detecting the voltage across the coil 2 is also connected to the power supplying coil 2. The output of the voltage detector 4 is connected to the power voltage regulator 5. A signal generator 7 and a received signal detecting element 8 are-connected to the signal transmitting/receiving coil 6.
The operation of the conventional non-contact portable carrier 9 will be described with specific reference to a flow chart shown in FIG. 7. As the non-contact portable carrier 9 is set on the terminal device 1, the power receiving coil 10 of the portable carrier 9 is brought close to the power supplying coil 12 of the terminal device 1. As a consequence, AC voltage is supplied from the power source 3 to the portable carrier 9 through the power supplying coil 2. This AC voltage is rectified into a DC voltage through the full-wave rectifier circuit 11 and the capacitor 12 and the DC voltage is supplied to the IC 13, whereby the portable carrier 9 is started in Step 51 of the flow.
In Step 52, the IC 13 of the portable carrier 9 turns the signal transmitting element 16 on and off, thus delivering to the terminal device 1 a start-up acknowledgment signal indicative of the start-up of the portable carrier 9, through the signal transmitting/receiving coil 14.
Upon detection of the start-up acknowledgment signal through the signal transmitting/receiving coil 6 and the received signal detecting element 8, the terminal device 1 drives the signal generator 7 as needed to transmit, through the coil 6, a signal indicative of the content of the processing and data.
In Step 53, the portable carrier 9 waits until it receives a the signal from the terminal device 1 through the coil 14 and the received signal detecting element 15. Until the signal is received, the output of Step 53 is "no" and Step 53 is repeated. Upon receipt of this signal, the output of Step 53 is "yes" and the process proceeds to Step 54 in which the the portable carrier 9 conducts a signal processing operation by means of IC 13 in Step 54. Namely, the portable carrier 9 conducts processing and control of data in accordance with the content of the received signal.
Then, in Step 55, the IC 13 of the portable carrier 9 turns on and off the signal transmitting element 16 as required, so as to deliver a signal indicative of the processing result or data to the terminal device 1 through the signal transmitting/receiving coil 14.
The above-mentioned steps 53 to 55 are repeatedly executed until Step 56 determines that the series of operations is completed. When the completion of operations is determined in Step 56, the process proceeds to Step 57 in which the supply of the AC voltage from the terminal device 1 is ceased so that the operation of the portable carrier 9 is terminated.
The portable carrier 9 consumes electrical power due to, for example, operation of the IC 13. In particular, a large power is consumed when the signal transmitting element 16 is turned on and off to deliver a signal to the terminal device 1 through the coil 14. In this operation, the load current in the power supplying coil 2 of the terminal device 1 is increased so that the voltage across this coil 2 is reduced. This voltage drop is detected by the voltage detector 4 so that the power voltage regulator 5 operates to increase the voltage across the coil 2 so as to compensate for the voltage drop.
Conversely, when the IC 13 and the signal transmitting element 16 of the portable carrier 9 do not operate, loads on the power supplying coil 2 of the terminal device 1 and the power receiving coil 10 of the portable carrier 9 are reduced, whereby the voltage of the smoothing capacitor 12, i.e., the voltage supplied to the IC 13, is elevated. This involves a risk of breakdown of the IC 13 due to application of a voltage exceeding the maximum rated voltage. This problem can be overcome by reducing the voltage across the power supply coil 2 by the operation of the voltage detector 4 and the power voltage regulator 5 in the terminal device 1. Such a measure, however, requires quite a delicate voltage control in the terminal device 1. Moreover, breakdown of the IC 13 due to instantaneous application of an over-voltage is unavoidable due to the delayed response of the voltage detector 4 and the power voltage regulator 5, even when the voltage across the coil 2 is controlled for the purpose of protecting the IC from breakdown.
Thus, the conventional non-contact portable carrier suffers from a problem in that the signal processing means, such as an IC, tends to be damaged due to the application of a high voltage, particularly when the power consumption in the portable carrier is small.